Electrical system



June 2, 1942. M A, W R 2,285,195

ELECTRICAL SYSTEM Filed Jan. 1, 1942 Inventor: Martin A. Edwards, by JV 5.x}

His Attorney Patented June 2, 1942 IUNTIVTEDK ELECTRICAL SYSTEM Martin A. Edwards, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application January 1, 1942, Serial No. 425,313

22- Claims.

My invention relates to electrical systems andin particular to dynamorneter control systems used in testing various types of prime movers.

An object of my invention is to provide an improved electrical system for the control of dynamometers. 7

Further objects andadvantages of my invention will become apparent and my invention will be better understood from the following descripeter of any suitable type, such as a direct current dynamometer provided with a commutator connected to the winding of the rotatable member II and having brushes l2 and 13 connected to a load including resistances I4 and IS. The -resistance section II of this load is substantially constant and the load on the machine is varied by changing the amount of resistance [5 included in the load circuit of the dynamometer. The dynamo-electric machine which forms the dynamometer is provided with a stationary field exciting winding I6 adapted to be energized by a main exciter which inherently limits the maximum load on the dynamometer. This main exciter is of the armature reaction excitation type and includes a rotatable member or an armature ll of the conventional direct current type provided with a winding and a commutator connected thereto. The primary excitation of this machine is provided by a main field exciting winding mary circuit through the armature winding of the exciter. This permits a current to fiow through the primary circuit of the armature winding which sets up an armature reaction indicated in the drawing by the arrow 24. As the armature rotates, the winding conductors cut the component of primary armature reaction and a voltage is generated between a set of secondary brushes 25 and 26. This secondary voltage causes an electric current to flow through the armature winding and energizes the field exciting winding iii of the main generator. A current limiting resistor 21 is arranged in series with the field exciting winding IS in order to limit the maximum energizing current of this field exciting winding. The fiow of current through the secondary circuit of the exciter armature winding ll produces a secondary component of armature reaction, represented by the arrow 28 in the drawing. which is opposed to the main field exciting winding component of energization represented by the arrow 29 in the drawing and provided by the field exciting winding I8. In order to minimize the current necessary to provide the controlling component of excitation 29, a compensating field exciting winding 30 is arranged on the exciter I! to provide a component of excitation along the secondary commutating axis of the exciter, represented by the arrow 3|, which is in opposition to the secondary armature reaction 28 and in the same direction as the main control component of excitation 29. The compensating field exciting winding 30 is energized by the secondary current of the main exciter, so that its energization is responsive to this secondary current and it is constructed and arranged so that the compensating component of excitation 3| is substantially equal and opposite to the secondary armature reaction 28, thereby efiectively neu- II which is connected to asubstantially conshort-circuitingconductor 23 electrically conlects together the primary brushes 2| and 22 oi the primary brush set so as to complete a pritralizing this component of magnetic excitation and minimizing the amount of control excitation required of the field exciting winding III. This increases the sensitivity of control of the entire system.

In this type system, it is desirable that the main load current of the main generator II should be limited to a maximum safe operating value. It is desirable that this should be inherent in the operation of the system, and in the illustratedarrangement this control feature is provided by a field exciting winding 32 arranged to provide a component of magnetic excitation along the secondary commutating axis of the main exciter l1 opposed to the control field exciting winding It, as indicated by the arrow 33. The energization of this field exciting winding 42 is provided by a diiierential voltage by connecting the terminals of this field excitingv winding across the substantially constant voltage source of electrical power supply It, as provided by the voltage across a potentiometer resistance 34 included between terminals 35 and 36 in opposition to the drop across the main load resistance section l4. The

potentiometer resistance 34 is connected directly across the separate source of electrical power supply It and the terminal 36 is -adiustable,- so that the drop across the resistance between the terminals 36 and 35 may be varied in order to vary the maximum load current on the main generator. A unidirectional current element 31, such'as a copper oxide rectifier is connected in series with the field exciting winding 32 and a terminal 38 of the main load resistor l4. Thus, if the voltage drop acrom the resistance i4 is greater than the voltage drop across the resistance I4 between the terminals 25 and 38, current will now .through the unidirectional element 31 and the field exciting winding 32 so as to energize this field exciting winding to provide a component of excitation, as indicated by the arrow 33,. thereby decreasing the resultant excitation along the secondary commutating axis of the main, exciter. ever, if the drop across the load resistance 14 is lower than the voltage drop across the resistance 84 between the terminals and 36, no

current will fiow through the field exciting winding 32 and it will remain deenergized, for the unidirectional element 31 will prevent a reversal of energizing current through this circuit. In this manner, the field exciting winding 32 will only be energized to decrease the excitation of the main exciter when the load on the main generator il exceeds a predetermined value, and this energizatlon will be responsive to the load current of the generator.

responsive auxiliary exciter II, no current flows through this circuit, as the unidirectional current element 4| will prevent the dew oi current. This unidirectional current element 4|, however. is arranged such that whenever the voltage of the auxiliary exciter ll. responsive to the speed of the main generator ll, exceeds the voltage drop across the resistance 42 between the terminals 43 and 44, current will-flow through this circuit and energize the field, exciting winding 48. The auxiliary excit'er 20 is constructed such that its voltage normally is greater than the drop to its normal operating speed, during which conditions the field exciting winding 48 is deenergized because of the low speed of the auxiliary How- In order to assure' the proper loading of the engine it by the generator II, it is desired that be a controllable factor and should be limited to a predetermined safe operating value. In order exciter- 39. This requires that the main field exciting winding l8 provide-an excitation equal to the main control component and, in addition, a component of excitation equal and opposite to the excitation 41 of the speed responsive field exciting winding 46. V

In order to assure stable operation of the excitation of this system, a field exciting winding 48 is arranged to provide a component of excitation along the secondary commutating axis of the main exciter l1 and is energized by connection across the secondary 49 of a transformer, the primary winding 50 of which is connected across the secondary terminals of the main exciter I1 and across the field exciting winding ii of the main generator ii. This connection of the field exciting winding 48 is such that any transient variations in the energization oi the main generator field excitingwinding It will induce a corresponding variation in the transformer secondary winding 49, and the field exciting winding 48 will produce a component of excitation 5| which will oppose the transient variations in the energization of the main generator field exciting winding It by inducing a voltage in the armature to obtain this result, an auxiliary or pilot exciter 39 is arranged to be driven through the engine generator shaft 40 at a speed having a predetermined speed relation to that of the engine In. and the generator II. This exciter 39 preferably is built as an unsaturated dynamo-electric machine and is excited by a field exciting winding 4| energized by the substantially constant voltage source of electrical power supply l9 so as to pro-- vide an electrical voltage which bears a substan-' ing 46 arranged to provide a component of magnetic excitation 41 along the secondary commutating axis of the main exciter il in opposition to the excitation 29 of the main field exciting winding 18. The potentiometer resistance 42 is connected across the substantially constant source of electrical power supply I9, such thatif the voltage drop across the part of the resistance 42 connected between the terminals 43 and 44 is greater than the voltage of the speed winding of the main exciter I! which will oppose such transient variations. The desired response of the main exciter H to 'all of the various components of excitation is obtained by driving this main exciter I! at a substantially constant speedby a constant speed source of mechanical power, such as a synchronous motor 52 which is mechanicallycoupled to the armature ll of the main exciter.

While I have illustrated and described a particular embodiment of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular arrangement disclosed,'and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical system including a main genprimary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting togeth- 2,2ss,19s.

er said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means for providing a component of excitation to said main exciter along the secondary commutating axis thereof in opposition to said main exciter first field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, and means including a second field exciting winding for providing a component of excitation responsive to the load current" of said main generator and along the secondary commutating axis of said main exciter in opposition to said main field exciting winding.

2. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a

set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means for providing a component of excitation to said citer in opposition to said main exciter first field exciting winding when the load current of said main exciter exceeds a predetermined value.

current of said main generator exceeds a predetermined value responsive to the load current of said main generator.

4. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a comutator connected thereto, a set of primary brushes and a slot of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connectingtogether said primary brushes to complete said primary circuit, means for connecting said secondary brushesto said main generator field exciting winding, means including a main field exciting winding for saidmain exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means including a second field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutat- 3. An electrical system including a main generator having a fieldexciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary'brushes and a set of secondary brushes displaced'about saidcommutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means including a "second field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter field exciting winding above a predetermined main generator speed responsiveto the speed of said main generator, a third field exciting winding arranged to provide a component of excitation along the secondary commutating axis of said main exciter in opposition to said exciter main field exciting winding, and means for energizing said third field exciting winding when the load ing axis thereof in opposition to said first main exciter field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, and means including a third field exciting winding for providing a component of excitation responsive to the load current of said main generator and along the secondary commutating axis of said main exciter in opposition to said exciter main field exciting winding when the load current of said generator exceeds a predetermined value.

5. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from 'said primary brushes for providing aprimary circuit and a secondaiy circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means for providing a'component of excitation to said main exciter along the secondary commutating axis thereof in opposition to said main exciter first field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, means including a second field exciting winding for providing a component of excitation responsive to the load current of said main generator and means for providing a component of excitation along the secondary commutating axis of said main exciter for opposing transient variations in the second- 4 said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for load current of main generator along the secondary commutating axis of said main exciter in opposition to said main exciter first field ex-' providing a component of excitation thereto ergizing said third field exciting winding when the load currentiof said main generator exceeds a'predetermined value responsive to the load curv '20 rent of said main generator.

7. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing. a component of excitation thereto along the secondary commutating axis thereof, means for providing a component of excitation to said main exciter along the secondary commutating axis thereof in opposition to said main exciter first field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, means including a second field exciting winding for providing a component of excitation responsive to the load current of said main generator and along the secondary commutating axis of said main exciter in opposition to said main field exciting winding, and means for providing a component of excitation along the secondary commutating axis of said main exciter for substantially neutralizing the armature reaction of said secondary circuit I citing winding when the load current of said main generator exceeds a predetermined value, and means for providing a component of excitation along thersecondary commutating axis of said main exciter for opposing transient variations in the secondary current of said main exciter responsive to the energization of said main generator field exciting winding.

9. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary -circuit respectively through' said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means for providing a component of excitation to said main exciter along the secondary commutating axis thereof in opposition to said main exciter first field exciting winding above a pre determined main generator speed responsive to the speed of said main generator, means for providing a component of excitation responsive to the load current of said main generator along the secondary commutating axis of said main exciter in opposition to said main exciter first field exciting winding when the load current of said main generator exceeds a predetermined value, and means for providing a component of excitation along the secondary commutating axis of said-main exciter for substantially neutralizing the armature reaction of said secondary circuit current in said main exciter armature.

10. An electrical system including a main generator having a field exciting winding, a, main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator fromsaid primary brushes for providing a primary circuit and a secondary circuit respectivel through said armature, means for connecting said secondary.

brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the sec ondary commutating axis thereof, a second field winding for said main exciter arranged to provide a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter first field exciting winding, means including a source of elecmain field exciting winding for said main exciter trical power supply responsive to the speed of said main generator and a substantially constant voltage source of electrical power supply arranged in opposition to each other for energizing said second field exciting winding, means for preventing the energization of said main exciter second field exciting winding above a predetermined main generator speed, a third field exciting winding arranged to provide a component of excitation along the secondary commutating axis of said main exciter in opposition to said main field exciting winding, and means for energizing said third field exciting winding responsive to the load current 01 said main generator when the load current of said main generator exceeds a predetermined value.

11. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set secondary brushes displaced about said commutator from said primar brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said seconda-ry brushes to'said main generator field excitr ing winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, a second field exciting winding for said main exciter arranged to provide a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter field exciting winding, means including an auxiliary exciter responsive to the speed of said main generator and a substantially constant voltage source of electrical power supply arranged in opposition to each other for energizing said second field exciting winding, means for preventing the energization of said second main exciter field exciting winding above a predetermined main generator speed, and means including a third field exciting winding for providing a com ponent of excitation along the secondary commutating axis of said main exciter in opposition to said exciter main field exciting winding when the load current of said main generator exceeds a predetermined value responsive to the current of said main generator.

12. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field excitingwinding, means including a main'field exciting winding for said a set of primary brushes and a set of secondary main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, a second field exciting winding for said main exciter arranged to provide a component of excitation thereto along the sec-' ondary commutating axis thereof in opposition to said main exciter first field exciting winding, means including an auxiliary exciter responsive to the speed of said main generator and a substantially constant voltage source of electrical power supply arranged in opposition to each other for energizing said second field exciting winding, means for preventing the energization of said second field exciting winding above a predetermined main generator speed, and means for providing a component of excitation responsive to the load current of said main generator and along the secondary commutating axis of said main exciter in opposition to said main field exciting winding when the load current of said main generator exceeds a predetermined value.

generator having a field exciting winding, 9. main exciter having an armature provided with a winding and a commutator connected thereto,

brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through 'said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means including a second field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, means including a third field exciting winding for providing a component of excitation responsive to the load current of said main generator:

and along the secondary commutating axis of said main exciter in opposition to said exciter main field exciting winding when the load current of said generator exceeds a predetermined value, and means including a fourth field exciting winding for providing a component of excitation along the secondary commutating axis of said mainexciter for substantially neutralizing armature reaction oi! secondary circuit current in said main exciter armature.

14. An electrical system including a main gen-- erator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto alongv the secondary commutating axis thereof, .means including a second field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, means including a third field exciting winding for providing a component of excitation responsive to'the load current of said main generator and along the secondary commutating axis of said main exciter in opposition to said exciter main field exciting winding when the load current of said generator exceeds a predetermined value, and means including a fourth field exciting winding for providing a component of excitation along the secondary commutating axis at said main exciter for opposing transient variations in the secondary current, thereof responsive to the energization of said main generator field exciting winding.

15. An electrical system including a main generator having a field exciting winding,- a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, a second field exciting winding for said main exciter arranged to provide a component of excitation thereto along the secondary commutating axis thereof in opposition to said main exciter'first field exciting winding, means including an auxiliary exciter responsive to thespeed of said main generator and a substantially constant voltage source of electrical power supply arranged in opposition to each other for en- 7 ergizing said second-field exciting winding, means for preventing the energization of said second field exciting winding above a predetermined main generator speed, means for providing a component of excitation responsive to the load current of said main generator and along the secondary commutating axis of said main exciter in opposition to said main field exciting winding when the load current of said main generator exceeds a predetermined value, and means for providing a component of excitation along the secondary commutating axis at said main exciter for opposing transient variations in the secondary current of said main exciter responsive to the energization of said main generator field exciting winding.

stantially neutralizing the armature reaction of said secondary circuit current in said main ex-.

erator having a field exciting winding, a main exciter having an armatureprovided with a winding and a commutator connected thereto, a

set-of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary, brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, means including a second field exciting winding for said main exciter for providing a component of excitationthereto along the secondary commutat'ing axis thereof in opposition to said first main exciter field exciting winding above a predetermined main generator speed responsive to the speed of said main generator, a third field exciting winding arranged to provide a component of excitation along the secondary commu- 16. An electrical system including a main -generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a

set of primary brushes and a setof secondary brushes displaced about said commutator from said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to-complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, a second field exciting winding for said main exciter arranged to provide a component of excitation thereto along the secondary commutating axis thereof in opposition to said main exciter first field exciting winding, means including an auxiliary exciter responsive to the speed of said main generator and a substantially constant voltage source of electrical powersupply arranged in opposition to each other for energizing said second field exciting winding, means for preventing the,energization of said second field exciting winding above a predetermined main generator speed, means for providing a component of excitation responsive to the load current of said main generator and long the secondary commutating-axis of said main exciter in opposition to said main field exciting winding when the load current of said main generator exceeds a predetermined value, and means for providing a component of excitation along the secondary V commutating axis of said main exciter for subtating axis of said main exciter in opposition to said exciter main field exciting winding, means for energizing said third field exciting winding when the load current of said main generator exceeds a predetermined value responsive to the i load current of said main generator, and means including a fourth field exciting winding for providing a component of excitation along the secondary. commutating axis of said, main exciter for opposing transient variations in the secondary current thereof responsive to the energization of said main generator field exciting winding.

18. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a

set of primary brushes and a set of secondary A exciter arranged to provide a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter field exciting winding, means ineluding an auxiliary exciter responsive to the determined main generator speed, means ineluding a third field exciting winding for providing a component of excitation along the secondary commutating axis oi. said main exciter in opposition to said exciter main field exciting winding when the load current of said main generator exceeds a predetermined value responsive to the current of said main generator, and means including a fourth field exciting winding for providing a component of excitation along the secondary commutating axis of said main exciter for substantially neutralizing armature reaction of secondary circuit current in said main exciter armature.

19. An electrical system including a main generator having a field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes and a set of secondary brushes displaced about said commutator from said primary brushes for providing aprimary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, a second field exciting winding for said main exciter arranged to provide a component of excitation thereto along the secondary commutating axis thereof in opposition to said first main exciter field exciting winding, means including an auxiliary exciter responsive to the speed of said main generator and a substantially constant voltage source of electrical power supply arranged in opposition to each other for energizing said second field exciting winding, means including an auxiliary exciter'responsive to the speed of said main generator and a substantially constant voltage source of electrical power supply arranged in opposition to each other for energizing said second field exciting winding, means for preventing the energization of said second exciter field exciting winding above a predetermined speed of said main generator, means including a third field exciting winding for providing a component of excitation responsive to the load current of said main generator and along the secondary commutating axis of said main exciter in opposition to said exciter main field exciting winding when the load current of said main generator exceeds a predetermined value, and means for providing a component of excitation along the secondary commutating axis of said main exciter for opposing transient variations in the secondary current thereof responsive to the energizaton of said main generator'field' exciting winding.

. 20. An electrical system including a main generator having a'field exciting winding, a main exciter having an armature provided with a winding and a commutator connected thereto, a set of primary brushes anda set of secondary brushes displacedabout said primary brushes for providing a primary circuit and a secondary circuit respectively through said armature, means for electrically connecting together said primary brushes to complete said primary circuit, means for connecting said secondary brushes to. said main generator field exciting winding, means including a main field exciting winding for said main exciter for providing a component of excitation thereto along the secondary commutating axis thereof, a second field exciting winding for said main. exciter arranged to provide a component oi excitation thereto along the secondary commutating axis thereo! in opposition to said first main exciter field exciting winding, means including an auxiliary exciter responsive to the speed of said main generator and a substantially constant voltage source of,electrical power supply arranged in opposition to each other for energizing said second field exciting winding, means including an auxiliary exciter responsive to the speed of said main generator and a substantially constant voltage source of electrical power sup-.- ply arranged in opposition to each other for energizing said second field exciting winding, means for preventing the energization of said second exciter field exciting winding above a predetermined speed of said main generator, means including a third field exciting winding for providing a component of excitation responsive to the load current of said main generator and along the secondary commutatingaxis of said main exciter in opposition to said exciter main field exciting winding when the load current of said main generator exceeds a predetermined value, means for providing a component of excitation along the secondary commutating axis of said main exciter for opposing transient vari: ations in the secondary current thereof responsive to the energization of said main generator field exciting winding, and means for providing a component of excitation along the secondary commutating axis of said main exciter for substantially neutralizing the armature reaction of said secondary circuit current in said main exciter armature.

21. An electrical system including a main generator having a field exciting winding, an exciter arranged to energize said main generator field exciting winding, means including a field exciting winding for providing the component of excitation to said exciter responsive to the speed of said main generator, means including a second field exciting winding for providing a component of excitation to said exciter responsive to the load current of said main generator and in the same direction as said first exciter field exciting winding arranged to be energized only when the load current of said main generator exceeds a predetermined value, and a third and main field exciting winding on said exciterior providing a component ,of excitation in opposition to said first and second exciter field exciting windings.

22. An electrical system including a main generator having a field exciting winding, an exciter arranged to energize said main generator field exciting winding, means including a field exciting winding for providing the component of excitation to said exciter responsive to the speed of said main generator, means including a second field exciting winding for providing a component of excitation to said exciter responsive to the load current of said main generator and in mam A. EDWARDS. 

